Can someone explain what the "Limiting Element Voltage" (LEV) is for a resistor is? and how you determine if your circuit is exceeding that rating?

I was picking out a resistor to use in a circuit I have and came across this rating on the datasheet. I was specifically looking at a 0402 SMT resistor with a rating of 50V for the limiting element voltage.

Specifically in the attached circuit. As Vin could be up to 60V are R1 and R3 resistors being exposed to a voltage above their 50V rating? and as such I would need to find a resistor with a higher LEV voltage ????


OR (for example with R3) is it simply using ohms law V=IR where I=.01A and R=169 so V=1.69 which is less than 50V so its ok?

 

R1 is in danger.

as for the rest, yes. Limiting Element Voltage is the highest voltage safe for that part.

 

R1 is in danger.

and is that because of OHMS law..Where R1 is doing 4mA(0.004A) * 15K = 60V (more than 50V)
But R3 is okay because .01A x 169 ohms = 1.69V (less than 50V) ?????

(except R1 is actually 1/2W which is a 1210 SMT package and has a 200V LEV rating)

 

Yes, R3 is fine.

Your simulation circuit is rather unusual in that you have the pulse source floating above ground. Is that true in the actual circuit?

 

Yes, R3 is fine.

Your simulation circuit is rather unusual in that you have the pulse source floating above ground. Is that true in the actual circuit?

SGT Wookie did that circuit for me a while back.. He said that for some reason LTSpice needed that R4 resistor there..but in reality its shouldn't be.. But I have removed it and put the source right to ground and didn't notice any real difference in the functionality of the circuit.

 

Thanks for covering this, crutschow. I had to go to work today and couldn't get back to clarify followup questions.

 

yes thanks to both of you.

 

What is the circuit supposed to do? It doesn't make sense to me.

 

A 60 volt pulse is limited by a constant current circuit so that it safely fires an optocoupler with a 10k pull up resistor on its open collector output.

 

A 60 volt pulse is limited by a constant current circuit so that it safely fires an optocoupler with a 10k pull up resistor on its open collector output.

The 9Meg resistor threw me. It would have 120kV across it, as would the optocoupler. I reread post #5, and understand that part now.
Apparently the input will (or can) go all the way to 60V, but the output needs to switch when the input is only a few volts. The current limiter protects the opto input, while consuming less power than a shunt limiter.
Is that the gist of it?

BTW, if the voltage across R1 is a problem, use two 7.5k resistors in series.

 

yes I need to pull a micro pin low when the input voltage is in the range of 5-60VDC

R1 really isn't a problem because its 1/2W which puts it into a 1210 SMT package which has a LEV of 200V versus a 0402 package with LEV of 50V

 

I don't know how much you are willing to pay for "better" performance, but check this out.